Question

cis-1-bromo-4-tert-butylcyclohexane and trans-1-bromo-4-tert-butylcyclohexane both react with sodium ethoxide in ethanol to give 4-tert-butylcyclohexene. However, one of the isomers reacts much more rapidly than the other isomer. Predict which isomer is reacting faster by showing a mechanism for each isomer. Your answer should account for the slower reacting substrate.

Answer 1

the cis isomer elimination is faster than trans isomer

in the stable conformation of cis isomer both H and Br are anti to each other. so anti periplanar transition state possible for fast elimination . so elomination is faster then tran isomer.

where as in the stable conformer of trans isomer H and Br are not anti to each other. It must get unstable and high energy conformer to get elimination. so elimination is slwer than cis isomer